Method and apparatus for separating fibrous suspensions in hydrocyclones



June 19, 1962 N. A. L. WIKDAHL METHOD AND APPARATUS FOR SEFARATINGFIBROUS SUSPENSIONS IN HYDROCYCLONES 3 Sheets-Sheet 1 Filed May 8, 1959June 19, 1962 N. A. L. WIKDAHL ,608

METHOD AND APPARATUS FOR E ARATING FIBROUS SUSPENSIONS IN HY CYCLONES 3Sheets-Sheet 2 Filed May 8, 1959 IN v/v rol? /V/1.s lQ/VDERS Anv/v/mrMzroewl- MCLM/ nun-of, firrak/vs rs June 19, 1962 N. A. L. WIKDAHLMETHOD AND APPARATUS FOR SEPARATING FIBROUS SIISPENSIONS INHYDROCYCLONEIS Filed May 8, 1959 FIGJ.

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m I Q 34 33 37 38 I/Vn/E/VTOI? HrroR/ws-yr United tates Patent 3,039,608METHOD AND APPARATUS FOR SEPARATING FIBROUS SUSPENSIONS IN HYDROCYCLONESNils Anders Lennert Wikdahl, Burevagen 16, Djursholm, Sweden Filed May8, 1959, Ser. No. 812,071 Claims priority, application Sweden May 8,1958 6 Claims. (Cl. 209--211) The present inventionrelates to a methodof separating or fractionating fibrous suspensions, preferablysuspensions of cellulose or wood pulp in hydrocyclones and to anapparatus for carrying out said method. Hydrocyclones are, as known,such devices which consist of a chamber having a circular cross sectionand at least one inlet and at least two outlets of which at least one isaxially arranged. Said hydrocyclones are provided with means forimparting to the suspension introduced a rotary motion around the axisof the chamber and the chamber is shaped in such a way that asubstantial part of the pressure energy supplied is transformed intorotary energy. A preferred embodiment of such a hydrocyclone comprises aconical chamber into which the suspension is introduced tangentially inthe wider portion of the chamber whereby vertical movements arisecausing the heavier or dynamically heavier particles (the coarserfraction) to leave the chamber through the apex. The lighter particles(the finer fraction) leave the chamber through a central outlet, theso-called overflow pipe.

In the cellulose and wood pulp industry the hydrocyclone plants arearranged in multiple steps, such as four or five steps. This means thatthe lighter fraction from one step except from the first step isreturned to the inlet of a preceding step and that the heavier fractionfrom one step is introduced into the inlet of a following step.Generally, the secondary steps do not improve the total separatingefiect of the plant. They serve in the first place to reduce the fibrelosses. For this reason the heavier fractions are pumped to a followingstep after dilution. Thus, diluting liquid and energy are supplied inorder to reduce the fibre losses and to make the plant more effective.

Said multiple step hydrocyclones are very complicated as each steprequires a pump and extensive pipe lines, motors, controlling means andso on. The pumps in the secondary steps are worn very much as in generalthe concentration of wearing particles increases for each step. Thus, alot may be gained if the number of steps can be reduced.

The present invention relates to a method by which the above mentionedinconveniences may be removed and by which a better fibre fractionationor separation may be obtained.

Accordingly, the present invention broadly consists in causing thefibrous suspension to pass through two or more choking members on itsWay towards the outlet for the heavier fraction and in supplying liquidat a pressure of 0.5 to 3.0 atmosphere gauge between the choking in sucha way that a cyclone action arises. The choking members are preferablymade of an elastic material such as rubber. In this case the chokingmembers may be expanded temporarily in order to prevent clogging. Theliquid introduced may be given a rotary motion in the same direction asthat of the suspension but may in some cases be given a directionopposite to that of the suspension. The liquid, such as water, may besupplied immediately after the choking members seen in the directiontowards the outlet for the heavier fraction. The apertures of thechoking members may have a different size so that the choking membersituated nearest to the inlet for the suspension has a larger aperturethan that of the following choking member.

The pressure of the liquid introduced between the choking members ispreferably lower than that of the suspension supplied, and is preferably0.1 to 3.4 kg./cm. lower, such as 0.5 to 2.0 kg./cm. lower. The liquidis supplied in general in a quantity of less than 50% of the suspensionprimarily supplied and preferably less than 20%.

The invention relates also to an apparatus for carrying out the abovedescribed method and said apparatus comprises a hydrocyclone which atthe outlet for the heavier fraction is provided with a housing dividedinto at least two chambers which are separated by choking members andeach chamber being provide with a tangential inlet for liquid.

The invention is more particularly described with reference to theaccompanying drawings in which FIG. 1 shows a longitudional section of ahydrocyclone,

FIG. 2 is a longitudinal section on a larger scale through the apexportion of the hydrocyclone,

FIG. 3 is a section along the line IIIIII of FIG 2,

FIG. 4 shows diagrammatically a conventional hydrocyclone plant, and

FIG. 5 is a hydrocyclone plant according to the present invention.

The hydrocyclone according to FIG. 1 comprises a lid 1 having an outlet2, the so-called overflow pipe, for the finer fraction, and inlet 3 forthe suspension to be treated and a conical portion 5 having an outletfor the coarser fraction. The apex of the conical portion 5 is providedwith a housing 6, more specifically shown in FIG. 2. The housing 6consists of a cylindrical casing in which another cylindrical casing 7is situated. The casing 7 is divided into three chambers 9, 10 and 11 bymeans of choking members 8, and is kept at a distance from the innerwall of the outer casing by means of spacing elements 12. Liquid may besupplied to the space between said casings by a tubular extension '13 ofsoft rubber having a central aperture. In the wall of the casing 7 thereare provided aperatures '14 tangentially connected to the inner wall ofthe casing 7 in the neighborhood of the choking members 8. The height ofthe chambers 9, 10 and 11 shall be larger than the diameter of thechambers.

The suspension to be treated is introduced under pressure by means ofthe inlet 3 into the wider portion of the cyclone and is imparted acyclone movement towards the apex of the cyclone. The coarser particlesmove downwards along the periphery towards the apex and the finer ascendin the vortex formed in the interior of the cyclone and leave throughthe overflow pipe 2. The coarser particles pass into the chamber 9 andwill there meet water supplied by the tubular extension 13- whereby afurther separation of the coarser particles takes place due to thearising cyclone action. In the same manner a repeated fractionationoccurs in the chambers 10 and 11. In this way a further part of thefiner fraction separated in the conical portion of the cyclone, whichfraction has been further treated in the chambers 9, 10, 11, is returnedto the outlet 2 thus reducing the fibre losses.

In FIG. 4 is shown a conventional hydrocyclone plant which comprisesthree groups of hydrocyclones 21, 22 and 23. The suspension to betreated is introduced through a pipe 24 into the cyclone 21. Theresulting finer fraction is discharged through a pipe 25 and the coarserfraction through a pipe 26 and is introduced into the cyclone 22.Therefrom the finer fraction is pumped through the pipe 24 to thecyclone 21. The coarser fraction leaving the cyclone 22 is fed to thecyclone 23 through the pipe 27 and the finer fraction obtained incyclone 23 is introduced into the cyclone 22 through a pipe 28. 'Thecoarser fraction leaving the cyclone 23 is discharged through a pipe 29.

The plant shown in FIG. 5 which is carried out according to the presentinvention, is with regard to the capacity 'is fed from a vessel 33 via apump 34 and a pipe 35 to the cyclones 31 and the finer fraction leavesthrough a pipe 36. The coarser fraction is fed to a vessel 37 and isintroduced via a pump 38 into the hydrocyclones 32 made in accordancewith the present invention, i.e. they are provided with a housing 39containing three chambers connected to the apices of the cyclones. Thefiner fraction obtained is returned to the vessel 33 through a pipe 40.Water is introduced into the housing 39 through a pipe 41. I,

In certain cases the hydrocyclones according to the invention may havean inferior separating capacity than conventional cyclones. In suchcases excellent results are obtained if conventional hydrocyclones areused in the first step and the coarser fraction from said step isintroducted into a second step using hydrocyclones in accordance withthe present invention as disclosed in FIG. 5.

Having now described my invention, what I claim as new and desire tosecure by Letters Patent is:

1. A method of separating or fractionating fibrous suspensions in ahydrocyclone chamber having a circular cross section comprising, thestep of: introducing a suspension tangentially under pressure into thehydrocyclone chamber to form a vortex, dividing the suspension in thevortex into a lighter ascending fraction and a heavier apex fraction,discharging each of the lighter and heavier fractions through individualaxially aligned outlets, further treating the heavier fraction byconstricting said heavier fraction from its individual axial outlet inat least two choking members, and passing a liquid under a pressure of0.5 to 3.0 atmosphere gauge tangentially at a point intermediate thechoking members to impart a cyclone action increasing the rotationalspeed of the heavier fraction.

2. A method according to claim 1 wherein the liquid is introducedbetween the choking members at a pressure which is 0.1 to 3.4 kg./cm.lower than the pressure of the fibrous suspension introduced.

3. A method according to claim 1 wherein the liquid is introducedimmediately downstream from the choking members.

4. Apparatus for separating or fractionating fibrous suspensionscomprising a hydrocyclone having an outlet for a heavier fraction, saidoutlet including a housing divided into at least two seperate chambersseparated by choking members, each one of said chambers being providedwith a tangential inlet for introducing liquid into the interior thereofduring passage of the heavier fraction passing into said hous ng toimpart a cyclone action increasing the rotational speed of the heavierfraction.

5. A method of separating fibrous material from solids intermingledtherewith by means of a hydrocyclone assembly, said method comprisingthe steps of tangentially feeding under pressure a liquid suspension ofsaid fibrous material and solids into a first chamber of said assemblyto form in said chamber a spirally rotating flow in which liquidenriched with fibrous material flows centrally upwards and liquidenriched with solids flows peripherally downwards, directing thedownward flow through a constriction into a second chamber of theassembly, feeding liquid under a pressure of 0.5 to 3.0 atmospheretangentially into said second chamber to impart to the enriched liquidin said chamber a renewed spirally rotating fiow in which liquidenriched with fibrous materials again flows centrally upwards and liquidenriched with solids again flows peripherally downwards, and dischargingthe liquid fiows enriched with solids at the base of the hydrocycloneassembly and the liquid flows enriched with fibrous material at the topof the hydrocyclone assembly.

6. An installation for a multiple stage separation of fibrous materialfrom solids intermingled therewith, said installation comprising ahydrocyclone including an elongated first housing of rotation ofsymmetric cross section, an inlet duct tangentially communicating withsaid first housing for feeding a pressure flow of a liquid suspension offibrous material and solids into said first housing and to impart tosaid flow a spirally rotating motion within the first housing, adischarge duct connected to the top of said first housing to dischargetherefrom liquid enriched with fibrous material, said hydrocycloneconstituting the first separation stage, an elongated second housing ofrotation of symmetric cross section disposed beneath said first housingcoaXially therewith, one end of said second housing communicating withthe base of said first housing to discharge therefrom liquid enrichedwith solids but still containing fibrous material into saidsecond-housing transverse partition walls dividing said second housinginto several chambers, each of said partition walls including anorifice, said orifices and the communication between the first housingand the second housing of the hydrocyclone being disposed in alignment,an inlet duct tangentially communicating with each of said secondhousing chambers for tangentially feeding liquid under pressure into therespective chamber to' impart spirally rotating motions to the liquid inthe chambers, and a discharge duct communicating with the base of thelowermost chamber to discharge therefrom liquid enriched with solids andsubstantially liberated from fibrous material, each of said chambersconstituting a further separation stage.

References Cited in the file of this patent UNITED STATES PATENTSRietema June 4, 1957

